The present invention relates to a centrifuge with a self-emptying drum with ejection openings in its jacket that lead out of a solids space and can be blocked off with a piston valve, with a closure compartment that can be charged with closure fluid and is associated with the piston valve, with part of the closure compartment being divided into an upper and a lower division, and with outflow channels leading out of the drum from the lower division of the closure compartment.
A centrifuge of this type is known from German Pat. No. 1 432 760. Its outflow channels leading out of the drum from the lower division of the closure compartment can be blocked off or uncovered with a hydraulic valve, the outflowing closure fluid automatically keeping the valve open. Thus, the valve cannot be closed until as much of the closure fluid as possible has flowed out. The closure compartment can therefore not be filled up again until the closure-fluid valve is closed again.
Self-emptying drums are preferably operated in such a way that only some of their contents are expelled when they are emptied without interrupting the supply of material to be centrifuged. To prevent the drum from opening automatically subsequent to emptying, the pressure below the piston valve must be restored more rapidly than that within the drum as it fills up. This is possible only if the closure compartment fills up again rapidly subsequent to emptying. With known drums, however, there is a delay until the lower division of the closure compartment has emptied. This type of drum can accordingly be emptied only when the material-supply inlet is closed.
Filling at least the upper division of the closure compartment before the closure-fluid valve closes through a special device that conveys the closure fluid into that division first has been proposed. In this case as well, however, the total closure compartment cannot be filled until the closure-fluid valve is closed. This also entails the risk that the pressure inside the drum will be restored more rapidly than that in the closure compartment. Decelerating the pressure buildup in the closure compartment also means the same thing as slow closure. This makes it impossible to obtain a piston-valve stroke that is as high as possible when the drum is emptied partially. When the piston valve goes through a partial-opening motion, however, optimum solids extraction is impossible because the small total ejection-opening cross-section freed by the piston valve does not allow the rings of solids to break up.